Sprint-interval training-induced alterations of Myosin heavy chain isoforms and enzyme activities in rat diaphragm: effect of normobaric hypoxia

Chronic intermittent hypoxia induces the pyroptosis of renal tubular epithelial cells by activating the NLRP3 inflammasome

Obstructive sleep apnea syndrome (OSAS) is a respiratory disorder and chronic intermittent hypoxia (CIH) is an important pathological characteristic of OSAS. Injuries on renal tubular epithelial cells were observed under the condition of CIH. Pyroptosis is a programmed mode of cell death following cell apoptosis and cell necrosis, which is mediated by NLRP3 signaling. The present study aims to investigate the effects of CIH on the pyroptosis of renal tubular epithelial cells and the underlying mechanism. Firstly, CIH was induced in two renal tubular epithelial cell lines, HK-2 cells and TCMK-1 cells. As the aggravation of hypoxia, an increasing trend of elevated apoptotic rate was observed in HK-2 cells and TCMK-1 cells, accompanied by the excessive release of ROS and LDH, and upregulation of NLRP3. Subsequently, the CIH model was established on rats. The pathological analysis results indicated that in CIH rats, the glomerular bottom membrane and mesangium were slightly thickened and edema was observed in the renal tubule epithelium. More serious injury was observed in the moderate intermittent hypoxia group. The expression level of IL-1β and IL-18 was promoted as the aggravation of hypoxia, accompanied by the elevated production of LDH and ROS. The expression level of cleaved Caspase-1, Caspase-1, GSDMD, TLR4, MyD88, NF-κB, p-NF-κB, and NLRP3 was found significantly upregulated as the aggravation of hypoxia. Lastly, the pathological changes in rats induced by CIH were dramatically abolished by MCC950, a specific inhibitor of NLRP3. Collectively, CIH triggered the pyroptosis of renal tubular epithelial cells by activating the NLRP3 inflammasome.

Effects of Respiratory Muscle Endurance Training in Hypoxia on Running Performance

PURPOSE

We hypothesized that respiratory muscle endurance training (RMET) in hypoxia induces greater improvements in respiratory muscle endurance with attenuated respiratory muscle metaboreflex and consequent whole-body performance. We evaluated respiratory muscle endurance and cardiovascular response during hyperpnoea and whole-body running performance before and after RMET in normoxia and hypoxia.

METHODS

Twenty-one collegiate endurance runners were assigned to control (n = 7), normoxic (n = 7), and hypoxic (n = 7) groups. Before and after the 6 wk of RMET, incremental respiratory endurance test and constant exercise tests were performed. The constant exercise test was performed on a treadmill at 95% of the individual's peak oxygen uptake (V˙O2peak). The RMET was isocapnic hyperpnoea under normoxic and hypoxic conditions (30 min·d). The initial target of minute ventilation during RMET was set to 50% of the individual maximal voluntary ventilation, and the target increased progressively during the 6 wk. Target arterial oxygen saturation in the hypoxic group was set to 90% in the first 2 wk, and thereafter it was set to 80%.

RESULTS

Respiratory muscle endurance was increased after RMET in the normoxic and hypoxic groups. The time to exhaustion at 95% V˙O2peak exercise also increased after RMET in the normoxic (10.2 ± 2.4 to 11.2 ± 2.6 min) and hypoxic (11.5 ± 2.6 to 12.6 ± 3.0 min) groups, but not in the control group (9.6 ± 3.2 to 9.4 ± 4.0 min). The magnitude of these changes did not differ between the normoxic and the hypoxic groups (P = 0.84).

CONCLUSION

These results suggest that the improvement of respiratory muscle endurance and blunted respiratory muscle metaboreflex could, in part, contribute to improved endurance performance in endurance-trained athletes. However, it is also suggested that there are no additional effects when the RMET is performed in hypoxia.

Expression of ammonia transporters Rhbg and Rhcg in mouse skeletal muscle and the effect of 6-week training on these proteins

The purposes of our study were to examine (1) Rh B glycoprotein (Rhbg) and Rh C glycoprotein (Rhcg) expressions in mouse skeletal muscle; and (2) the effect of 6-week training on Rhbg and Rhcg expressions. The levels of Rhbg and Rhcg expressions were much higher in the soleus (Sol) than in the plantaris (Pla) or gastrocnemius (Gas). Immunofluorescence microscopy demonstrated that Rhbg colocalizes with dystrophin, a plasma membrane protein marker, whereas Rhcg colocalizes with CD31, a vascular endothelial cell marker. In a 6-week swim training study, we set up two different training groups. Endurance (END) group underwent swim training without load for 30 min and exercise time was increased by 30 min every 2 weeks. High-intensity interval training (HIIT) group underwent 10–12 sets of swim training at 20 sec per set and intervals of 10 sec, with a load of 10% body weight. After 6 weeks of training, all mice performed exhaustive swimming performance test (PT), with 9% of body weight to exhaustion. HIIT group could significantly swim more and showed significantly lower blood ammonia level compared with control (CON) group at immediately after PT. Rhbg and Rhcg levels did not change after 6 weeks in both END and HIIT groups. Our results indicate that ammonia transporters are more abundant in slow fiber than fast fiber muscles and 6 weeks swim training suppresses blood ammonia elevation induced by high-intensity exercise with performance improvement, although the levels of ammonia transporter proteins does not change.

High-intensity interval training increases intrinsic rates of mitochondrial fatty acid oxidation in rat red and white skeletal muscle

High-intensity interval training (HIIT) can increase mitochondrial volume in skeletal muscle. However, it is unclear whether HIIT alters the intrinsic capacity of mitochondrial fatty acid oxidation, or whether such changes are associated with changes in mitochondrial FAT/CD36, a regulator of fatty acid oxidation, or with reciprocal changes in the nuclear receptor coactivator (peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1α)) and the corepressor (receptor-interacting protein 140 (RIP140)). We examined whether HIIT alters fatty acid oxidation rates in the isolated subsarcolemmal (SS) and intermyofibrillar (IMF) mitochondria of red and white skeletal muscle and (or) induces changes in muscle PGC-1α and RIP140 proteins and mitochondrial FAT/CD36 protein content. Rats were divided into untrained or HIIT-trained groups. HIIT animals performed 10 bouts of 1-min high-intensity treadmill running (30–55 m·min–1), separated by 2 min of rest, for 5 days a week for 4 weeks. As expected, after the training period, HIIT increased mitochondrial enzymes (citrate synthase, COXIV, and β-hydroxyacyl CoA dehydrogenase) in red and white muscle, indicating that muscle mitochondrial volume had increased. HIIT also increased the rates of palmitate oxidation in mitochondria of red (37% for SS and 19% for IMF) and white (36% for SS and 12% for IMF) muscle. No changes occurred in SS and IMF mitochondrial FAT/CD36 proteins, despite increasing FAT/CD36 at the whole-muscle level (27% for red and 22% for white). Concurrently, muscle PGC-1α protein was increased in red (22%) and white (16%) muscle, but RIP140 was not altered. These results indicate that increases in SS and IMF mitochondrial fatty acid oxidation induced by HIIT are accompanied by an increase in PGC-1α, but not RIP140 or FAT/CD36.

Living at high altitude in combination with sea-level sprint training increases hematological parameters but does not improve performance in rats

The regimen of aerobic training at sea level with recovery at high altitude has been used by athletes to improve performance. However, little is known about the effects of hypoxia when combined with sprint interval training on performance. The aim of the present study was to determine the effect of a "living high-sprint training low" strategy on hemoglobin, hematocrit and erythropoietin levels in rats. We also wanted to test whether the addition of a hypoxic stress to the program of daily treadmill running at high speeds induces expressional adaptations in skeletal muscle and affects performance. The protein content of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), cytochrome C, pyruvate dehydrogenase kinase (PDK1), heat shock protein 70 (HSP70), manganese superoxide dismutase (MnSOD) and citrate synthase activity were determined in different muscle fiber types in our animals (red and white gastrocnemius muscle). We also determined the maximal aerobic velocity (MAV) before and after the training period. A total of 24 male Wistar rats (3 month old) were randomly divided into four experimental groups: the normoxic control group (n = 6), the normoxic trained group (n = 6), the hypoxic control group (12 h pO(2) 12%/12 h pO(2) 21%) (n = 6) and the hypoxic trained group (12 h pO(2) 12%/12 h pO(2) 21%). Living in normobaric hypoxia condition for 21 days significantly increased hemoglobin, hematocrit and erythropoietin levels in both the rest and the trained groups. The trained animals (normoxia and hypoxia) significantly increased their maximal aerobic velocity. No changes were found in the skeletal muscle in PGC-1α, cytochrome C, PDK1, HSP70, MnSOD protein content and in the citrate synthase activity in any experimental group. Regardless of whether it is combined with sprint interval training or not, after 21 days of living at high altitude we found a significant increase in the hematological values determined in our study. However, contrary to our starting hypothesis, the combination of normobaric hypoxia and sprint training did not improve MAV in our animals.

Different adaptations of alpha-actinin isoforms to exercise training in rat skeletal muscles

AIM

Alpha (alpha)-actinins are located in the skeletal muscle Z-line and form actin-actin cross-links. Mammalian skeletal muscle has two isoforms: alpha-actinin-2 and alpha-actinin-3. However, the response of alpha-actinin to exercise training is little understood. Therefore, the current study examined the effects of exercise training on the expression level of two alpha-actinin isoforms in skeletal muscles.

METHODS

Twelve male Wistar rats were assigned randomly to a control (C; n = 6) or exercise training (T; n = 6) group. After T animals were trained on an animal treadmill for 9 weeks, alpha-actinin-2 and alpha-actinin-3 levels in the plantaris, white and red gastrocnemius muscles were analysed. In addition, changes in the myosin heavy chain (MyHC) composition were assessed, and muscle bioenergetic enzyme activities were measured.

RESULTS

Results show that exercise training increased alpha-actinin-2 expression levels in all muscles (P < 0.05). However, no significant difference was found in alpha-actinin-3 expression levels between C and T animals. Subsequent MyHC analyses of all muscle showed an MyHC shift with direction from IIb to IIa. Furthermore, enzymatic analysis revealed that exercise training improved enzyme activities related to aerobic metabolism.

CONCLUSION

The results of this study demonstrate that exercise training alters the expression level of alpha-actinin at the isoform level. Moreover, the increase in expression levels of alpha-actinin-2 is apparently related to alteration of skeletal muscle: its aerobic capacity is improved.

Microwave hyperthermia treatment increases heat shock proteins in human skeletal muscle

OBJECTIVE

To test the hypothesis that microwave hyperthermia treatment (MHT) increases heat shock proteins (HSPs) in the human vastus lateralis muscle.

METHODS

Four untrained healthy male volunteers participated in this study. The lateral side of the thigh of one leg (heated leg) was heated with a microwave generator (2.5 GHz, 150 W) for 20 min. At 1 day after the MHT, a muscle sample was taken from the heated leg. A control sample was taken from the unheated leg on another day of the MHT. For both legs, HSP90, HSP72 and HSP27 levels were compared.

RESULTS

The HSP90, HSP72 and HSP27 levels in heated legs were significantly higher than those in control legs (p<0.05).

CONCLUSIONS

Application of MHT can increase the levels of several HSPs in human skeletal muscle.